1. Field of the Invention
The present invention relates to a sheet to form a protective film for chips, which enables to efficiently form a protective film on a back surface of a semiconductor chip, and thereby contributes to improvement in production efficiency of chips. More particularly, the present invention relates to a sheet to form a protective film for chips, which is used in production of semiconductor chips by face down mounting process.
The present invention also relates to a process for producing semiconductor chips, using the sheet to form a protective film for chips.
2. Description of the Prior Art
Recently, production of semiconductor devices is made through a so-called face down mounting process. In the face down process, chips are electrically connected with a substrate through a convex portion (bump) formed on a circuit surface of the chip to ensure its conductivity to the substrate.
Semiconductor devices are generally produced though the following steps:
(1) forming a circuit on a surface of a semiconductor wafer by etching or the like and providing a bump on the appointed position of the circuit surface;
(2) grinding the back surface of semiconductor wafer to have a given thickness;
(3) fixing the back surface of semiconductor wafer onto a dicing sheet which is tautly supported by a ring frame, and dicing the wafer to separate each circuit by the use of a dicing saw to obtain semiconductor chips; and
(4) picking up the semiconductor chips to mount them face down on a prescribed substrate and sealing the chip in a resin or coating the back surface of chip with a resin according to necessity for chip protection, thereby obtaining a semiconductor device.
The resin sealing is performed by dripping resin in a proper amount on the chip (potting method) or using a mold (molding method), both followed by curing. The potting method has a drawback of difficulty in dripping a proper amount of resin. The molding method involves washing of the mold, which will require additional costs for equipment and operation thereof.
The resin coating may cause ununiform quality because of the difficulty in spreading a proper amount of resin evenly on the chips.
Therefore, the technique which is capable of forming a highly uniform protective film on a back surface of chip by simplified operation, has been desired.
In the grinding of the back surface of the wafer in step (2), minute streaky scratches are formed on the back surface of the chip owing to the use of a grinding machine. The minute scratches may cause cracks during the dicing in step (3) or after the device is packaged. As such, it has been conventionally required in some cases to perform chemical etching after the mechanical grinding to eliminate the minute scratches. The chemical etching, as a matter of course, raises problems related to the cost increase for its equipment and operation.
Therefore, the technique for prevailing adverse effects resulting from minute scratches has been desired, even if minute scratches are left on the back surface of wafer as a result of mechanical grinding.
In light of the above prior art, it is an object of the present invention to provide a process through which a highly uniform protective film can be readily formed on a back surface of chip, and, even if minute scratches are formed on the back surface of chip as a result of mechanical grinding, the chip is prevailed over adverse effects resulting from the scratches. It is another object of the invention to provide a sheet to form a protective film for chips employable in the above process.